[InstCombine] Make cttz/ctlz knownbits tests more robust; NFC

Comments

[InstCombine] Make cttz/ctlz knownbits tests more robust; NFC
Tests checking for the addition of !range metadata should be
preserved if cttz/ctlz + icmp is optimized.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349318 91177308-0d34-0410-b5e6-96231b3b80d8